. >> reporter: president obama looked relaxed this week. mitt romney, too. but he knows he has to change perceptions tonight. more voters now see romney negatively than see him positively. and that loses elections. >> only two presidential candidates in the last 20 years have had a net negative image at this point and one of them lost, george h.w. bush. >> reporter: romney got good news from three battlegrounds in florida. he's now behind by just one point. still way down in ohio. but in virginia, romney's down by just two. with a lot on the line in past debates, romney's done well. >> going up against mitt romney is not a fun thing. he's got the facts. he drills you, stays, tenacious. >> reporter: and sometimes aggressive. >> don't use a term like that. >> reporter: aides admit barack obama in debates can sound like a professorial know it all. >> i understand the broader point that senator clinton has been trying to make over the last several weeks. >> reporter: tonight's format is from 2008, two podiums, moderator jim lehrer, 90 minutes, no breaks. a back-